Stargazers around the world were treated on Wednesday night to the rare sight of a "blue supermoon" -- a full moon which came unusually close to the earth, making it seem larger and brighter in the night sky.

A "blue moon" comes around only -- well, once in a blue moon. A moon is said to be "blue" when it is the second full moon to occur in a calendar month. This event -- when a year sees 13 full moons rather than the ordinary 12 -- occurs once every two or three years.

But a "blue supermoon" is an even rarer lunar event. Not only did Wednesday night see the second full moon of August -- but it came at its closest point in its orbit around Earth. This "supermoon" came nearly 18,000 miles closer to the Earth than its normal distance, cutting a more imposing figure on the night sky than usual.

The last blue supermoon was in 2009, according to NASA -- and the next is not expected until 2037.

Hikers watch the super blue moon from the summit of Piestewa Peak in Phoenix, US, on August 30.
Hikers watch the super blue moon from the summit of Piestewa Peak in Phoenix, US, on August 30.
Rob Schumacher/The Republic/Reuters
The super blue moon rises over El Pilar Basilica in Zaragoza, Spain, on August 30.
The super blue moon rises over El Pilar Basilica in Zaragoza, Spain, on August 30.
Javier Belver/AEPA-EFE/Shutterstock
The super blue moon rises behind a statue of Latin American Liberator Simon Bolivar in Caracas, Venezuela, on August 30.
The super blue moon rises behind a statue of Latin American Liberator Simon Bolivar in Caracas, Venezuela, on August 30.
Federico Parra/AFP/Getty Images
A woman takes pictures of a super blue moon rising above Lisbon, Portugal, on August 30.
A woman takes pictures of a super blue moon rising above Lisbon, Portugal, on August 30.
Armando Franca/AP
The super blue moon sets behind the CN tower in Toronto, Canada, on August 30.
The super blue moon sets behind the CN tower in Toronto, Canada, on August 30.
Frank Gunn/AP
The super blue moon rises behind the Temple of Poseidon, near Athens, Greece, on August 30.
The super blue moon rises behind the Temple of Poseidon, near Athens, Greece, on August 30.
Stelios Misinas /Reuters
A man rides a bicycle as the super blue moon rises over the northern town of Beit Lahia in the Gaza Strip on August 30.
A man rides a bicycle as the super blue moon rises over the northern town of Beit Lahia in the Gaza Strip on August 30.
Mohammed Abed/AFP/Getty Images
The blue super moon rises over Havana, Cuba, on August 30.
The blue super moon rises over Havana, Cuba, on August 30.
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An aircraft passes in front of a rare super blue moon, in London, England, on August 30.
An aircraft passes in front of a rare super blue moon, in London, England, on August 30.
Peter MacDiarmid/Shutterstock
The super blue moon sets close to St. Basil's Cathedral, in Red Square, Moscow, Russia, on August 30.
The super blue moon sets close to St. Basil's Cathedral, in Red Square, Moscow, Russia, on August 30.
Alexander Zemlianichenko/AP
The super blue moon rises behind the small village of Ujue, northern Spain, on August 30.
The super blue moon rises behind the small village of Ujue, northern Spain, on August 30.
Alvaro Barrientos/AP
Visitors stop to take pictures of a waxing gibbous moon at 96% illumination at Fort Baker in Sausalito, California, on August 29.
Visitors stop to take pictures of a waxing gibbous moon at 96% illumination at Fort Baker in Sausalito, California, on August 29.
Jose Carlos Fajardo/Bay Area News Group/AP
The super blue moon rises behind Castel del Monte Castle in Andria, Puglia, Italy, on August 29.
The super blue moon rises behind Castel del Monte Castle in Andria, Puglia, Italy, on August 29.
Lorenzo Di Cola/NurPhoto/Getty Images